Field of the Disclosure
This disclosure relates to connections between downhole tubulars, such as drill pipe tool joints or connections. More particularly, this disclosure relates to methods and apparatuses for strengthening the connections between wired drill pipe (WDP) joints.
Background of the Technology
In drilling by the rotary method, a drill bit is attached to the lower end of a drill stem composed of lengths of tubular drill pipe and other components that are joined together by connections with rotary shouldered threaded connections. In this disclosure, “drill stem” is intended to include other forms of downhole tubular strings such as drill strings and work strings. A rotary shouldered threaded connection may also be referred to as RSTC.
The drill stem may include threads that are engaged by right hand and/or left hand rotation. The threaded connections must sustain the weight of the drill stem, withstand the strain of repeated make-up and break-out, resist fatigue, resist additional make-up during drilling, provide a leak proof seal, and not loosen during normal operations.
The rotary drilling process subjects the drill stem to tremendous dynamic tensile stresses, dynamic bending stresses and dynamic rotational stresses that can result in premature drill stem failure due to fatigue. The accepted design of drill stem connections is to incorporate coarse tapered threads and metal to metal sealing shoulders. Proper design is a balance of strength between the internal and external thread connection. Some of the variables include outside diameter, inside diameters, thread pitch, thread form, sealing shoulder area, metal selection, grease friction factor and assembly torque. Those skilled in the art are aware of the interrelationships of these variables and the severity of the stresses placed on a drill stem.
The tool joints or pipe connections in the drill stem must have appropriate shoulder area, thread pitch, shear area and friction to transmit the required drilling torque. In use, all threads in the drill string must be assembled with a torque that exceeds the required drilling torque in order to handle tensile and bending loads without shoulder separation. Shoulder separation causes leaks and fretting wear. Relatively deeper wells require a greater amount of drilling torque to be applied to the drill string during drilling. In order to avoid uncontrolled downhole makeup of the drill string, the torque applied during makeup must be increased, thereby increasing the amount of stress on the RSTC connection. In response to this issue, double shouldered connections have been developed to better distribute stress generated from the makeup torque and apply it to the connection across a primary and a secondary shoulder of the RSTC. However, in the case of WDP, in order to transmit a signal along the length of the drill string, a groove is provided within the body of each tubular member of the drill string. This groove may extend through one of the shoulders of a double shouldered connection, forming a stress riser within the connection by reducing the surface area of the affected shoulder in the connection.
Accordingly, there remains a need in the art for an apparatus and methods for strengthening the connections between segments of drill pipe, particularly WDP. Such apparatuses and methods would be particularly well received if they could provide stronger connections in an efficient and relatively cost effective manner.